1. Field of the Invention
The present invention relates to a glass sheet processing system, and more particularly to a conveyor roller for a roller conveyor for conveying a heated glass sheet in such a glass sheet processing system.
2. Description of the Relevant Art
Systems for producing curved tempered glass sheets for use as window glass sheets on motor vehicles such as automobiles are disclosed in Japanese Patent Publications Nos. 58/3978 and 58/13502 and U.S. Pat. Nos. 4,272,274 and 4,421,482, for example. One typical method of shaping such a sheet glass includes the steps of heating a flat sheet to the softening point of glass at a heating station, shaping the heated glass sheet to a desired curvature at a shaping station, and then quenching the shaped glass sheet in a controlled manner to a temperature below the tempering temperature range of glass at a quenching station. The glass sheet heated at the heating station is delivered substantially horizontally to the shaping station by a plurality of conveyor rollers of a roller conveyor. The shaped sheet glass is likewise conveyed from the shaping station to the quenching station by a plurality of horizontal conveyor rollers spaced at intervals in the direction of feed. Each of these conveyor rollers comprises a core made of a ceramic material and a sleeve of glass fibers or aromatic polyamide fibers sold by E. I. Dupont de Nemours & Co., U.S.A. under registered U.S. trademark "Kevlar", the sleeve being wound around the core and attached at opposite ends to the core by an adhesive tape, as disclosed in U.S. Pat. No. 4,421,482. Japanese Patent Publication No. 58/13502 discloses another conveyor roller in which a sleeve of asbestos is fitted over a hollow core. The materials of the sleeve serve to make the conveyor roller resistant to heat. Use of the Kevlar fibers is advantageous in that their low thermal conductivity is effective in preventing chill cracking of a glass sheet conveyed by the conveyor rollers.
The conventional sleeves of the conveyor rollers have been in the form of woven cloth that causes some drawbacks. One of the shortcomings is that the woven cloth tends to leave cloth marks on the surface of the glass sheet being delivered by the conveyor rollers. The glass sheet therefore has small surface irregularities which are responsible for optical defects. The glass surface irregularities could be reduced by employing thinner fibers for the sleeve cloth. The sleeve cloth of thinner fibers would however become less durable and might be broken in use. Another deficiency is that when the sleeve cloth is cut off or broken by a glass edge or a broken glass piece, the sleeve cloth is unraveled progressively from the cut or broken region.